1. Field of the Invention
The present invention relates to a communication device which controls a device to be controlled based on reference timing that is acquired from reception data, shutter glasses which open and close shutters based on reference timing that is acquired from reception data, and a communication system which transmits and receives data that indicates reference timing.
2. Description of the Related Art
In a 3D video display system, a 3D-capable television apparatus and 3D glasses, or shutter glasses, communicate with each other so that the operation timing of the 3D-capable television apparatus will coincide with that of the 3D glasses. FIG. 1 schematically shows a conventional wireless communication system that is applicable to such a 3D video display system.
A transmitter 1 includes at least a control device 3 and a communication device 4. The control device 3 periodically generates data to be transmitted to a receiver 2, and generates a data transmission command for the communication device 4. The data to be transmitted includes data that indicates reference timing. The control device 3 also performs transmission and reception control on packets including data on the communication device 4. The communication device 4 transmits and receives packets through an antenna 4a according to commands from the control device 3.
The receiver 2 includes at least a communication device 5 and a display device 6. The communication device 5 receives transmission packets from the transmitter 1 through an antenna 5a. The communication device 5 extracts reception data from the packets and, if the data indicates reference timing, supplies a control signal synchronous with the detection of the reference timing to the display device 6. The display device 6 is a device that provides a display in synchronization with the reference timing transmitted from the transmitter 1. The display device 6 performs a display operation according to the control signal supplied from the communication device 5.
The operation of the transmitter 1 will be described. In the transmitter 1, a built-in timer (not shown) of the control device 3 measures predetermined cycles (interval period). When the measurement is completed, the control device 3 composes a transmission packet, issues a transmission command to the communication device 4, and transfers the transmission packet to the communication device 4. Receiving the transmission command and transmission packet from the control device 3, the communication device 4 modulates the transmission packet and sends out the resulting digital signal as an RF signal of a predetermined frequency.
Next, the operation of the receiver 2 will be described. In the receiver 2, a built-in timer of the communication device 5 measures predetermined cycles. When the measurement is completed, the communication device 5 receives the RF signal sent from the transmitter 1. The communication device 5 demodulates a reception signal corresponding to the RF signal into a digital signal, and extracts data in the packet from the digital signal.
The communication device 5 includes a control circuit that performs transmission and reception control of the communication device. When packet reception is completed, the control circuit analyzes the data in the packet and, if the data is determined to be destined to the own circuit, outputs a control signal for controlling the display device 6.
As shown in FIG. 2, in the transmitter 1, the aforementioned built-in timer of the control device 3 counts predetermined cycles (interval period). Each time the counting is completed, the transmitter 1 starts to transmit a packet that includes data notifying of the completion of the interval period. The receiver 2 receives the packet and, after a lapse of processing time of the foregoing control circuit, performs control on the display device 6 according to the data in the packet.
If such a wireless communication system is applied to a 3D video display system, the transmitter 1 is implemented on the 3D-capable television apparatus and the receiver 2 is implemented on the 3D glasses. The display device 6 corresponds to liquid crystal display devices of the 3D glasses (see Patent Literature 1). The transmitter 1 inserts a synchronization signal pattern that represents a synchronization signal into the packet as data to be transmitted. The control circuit discriminates the synchronization signal pattern by data analysis. When the result of data analysis shows that the packet data contains a synchronization signal pattern, the control circuit in the communication device 5 assumes the point in time to be the time of occurrence of a synchronization signal. As shown by full lines in FIG. 3, the control circuit generates a left shutter open/close signal and a right shutter open/close signal of the 3D glasses as respective control signals. The 3D glasses have liquid crystal shutters at positions where corresponding to right and left lenses of ordinary glasses. The right and left liquid crystal shutters can be individually opened and closed in response to the right shutter open/close signal and the left shutter open/close signal, respectively, which allows functioning as a pair of 3D glasses.    Patent Literature 1: Japanese Patent Kokai No. 2010-117437    Patent Literature 2: Japanese Patent Kokai No. H6-223035